In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers have included the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also have included the full character type wherein individual type elements are caused to be driven against a ribbon and paper or like record media adjacent and in contact with a platen.
The typical and well-known arrangement in a printing operation provides for transfer of a portion of the ink from the ribbon to result in a mark or image on the paper. Another arrangement includes the use of carbonless paper wherein the impact from a print wire or a type element causes rupture of encapsulated material for marking the paper. Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in manner and fashion so as to be machine readable in a subsequent operation. One of the known encoding systems is MICR (Magnetic Ink Character Recognition) utilizing the manner of operation as just mentioned.
While the impact printing method has dominated the industry, one disadvantage of this type of printing is the noise level which is attained during printing operation. Many efforts have been made to reduce the high noise levels by use of sound absorbing or cushioning materials or by isolating the printing apparatus.
More recently, the advent of thermal printing which effectively and significantly reduces the noise levels has brought about the requirements for heating of extremely precise areas of the record media by use of relatively low energy and thin film resistors. The intense heating of the localized areas causes transfer of ink from a ribbon onto the paper or like receiving substrate. Alternatively, the paper may be of the thermal type which includes materials that are responsive to the generated heat.
The use of thermal transfer printing, especially when performing a subsequent sorting operation, can result in smearing or smudging adjacent the printed symbols or digits on the receiving substrate. This smearing can make character recognition, such as OCR (Optical Character Recognition) or MICR (Magnetic Ink Character Recognition), difficult and sometimes impossible. Additionally, the surface of the receiving substrate and the printed symbols or digits are subject to scratching which can result in blurred images and incorrect reading of the characters.
The present invention provides a thermal transfer medium in the preferred form of a ribbon which eliminates or substantially reduces smearing or smudging and scratching across or adjacent the printed digits or symbols during sorting or other operations.
Representative documentation in the area of nonimpact printing includes U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, which discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a sensible dye or oxide pigment material.
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga et al. on Feb. 16, 1982, discloses a thermal transfer element comprising a foundation, a color developing layer and a hot melt ink layer. The ink layer includes heat conductive material and a solid wax as a binder material.
U.S. Pat. No. 4,403,224, issued to R. C. Wirnowski on Sep. 6, 1983, discloses a surface recording layer comprising a resin binder, a pigment dispersed in the binder, and a smudge inhibitor incorporated into and dispersed throughout the surface recording layer, or applied to the surface recording layer as a separate coating.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga et al. on Jul. 31 1984, discloses a heatsensitive magnetic transfer element having a hot melt or a solvent coating.
U.S. Pat. No. 4,523,207, issued to M. W. Lewis et al. on Jun. 11, 1985, discloses a multiple copy thermal record sheet which uses crystal violet lactone and a phenolic resin.
U.S. Pat. No. 4,628,000, issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer formulation that includes an adhesive-plasticizer or sucrose benzoate transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,687,701, issued to F. Knirsch et al. on Aug. 18, 1987, discloses a heat sensitive inked element using a blend of thermoplastic resins and waxes.
U.S. Pat. No. 4,698,268, issued to S. Ueyama on Oct. 6, 1987, discloses a heat resistant substrate and a heat-sensitive transferring ink layer. An overcoat layer may be formed on the ink layer.
U.S. Pat. No. 4,707,395, issued to S. Ueyama et al. on Nov. 17, 1987, discloses a substrate, a heat-sensitive releasing layer, `coloring agent layer, and a heat-sensitive cohesive layer.
U.S. Pat. No. 4,777,079, issued to M. Nagamoto et al. on Oct. 11, 1988, discloses an image transfer type thermosensitive recording medium using thermosoftening resins and a coloring agent.
And, U.S. Pat. No. 4,778,729, issued to A. Mizobuchi on Oct. 18, 1988, discloses a heat transfer sheet comprising a hot melt ink layer on one surface of a film and a filling layer laminated on the ink layer.